I agree with your parent. When I started with (Python) webdev some years ago I picked Flask, but nowadays I use Django, as it has superb documentation and useful things built-in. In particular I miss the user-management, authentication and authorization in Flask.
Personally I consider Django without any additional apps less complex than Flask with apps (or "plugins" in Flask jargon) to handle basic stuff like auth.
If performance is a concern, both of them are insufficient and I would rather pick another language like Rust, Go or even Java.
I started with Flask, moved to Django, and now at work am back on Flask. It all depends on what you are building; if you are going to need some ORM, standard auth, etc, Django is a no brainer. However if you are going to be building out much of your own idiosyncratic architecture, Flask gets out of your way and avoids including lots of things you don't need.
For performance, we are building some parts of our system with Clojure. It feels extremely well suited, albeit with some initial learning curve.
Personally I consider Django without any additional apps less complex than Flask with apps (or "plugins" in Flask jargon) to handle basic stuff like auth.
If performance is a concern, both of them are insufficient and I would rather pick another language like Rust, Go or even Java.